This invention relates to an impact collision, ion-scattering spectrometer. More specifically, the invention relates to an apparatus in which a sample is irradiated with an ion beam, whereby particles are caused to scatter from the sample, and the energy of those particles which scatter in an axial direction the same as that of the irradiating ion beam on the incident side of the beam is analyzed.
In many cases a time of flight spectrometer is used as means for analyzing energy in an impact collision, ion-scattering spectrometer. A time-of-flight spectrometer performs energy analysis based upon differences in time required for particles, which are scattered simultaneously from a sample, to reach a detector. The characterizing feature of a spectrometer of this type is that energy analysis is capable of being performed without taking account of whether the particles carry an electric charge.
The particles caused to scatter when a sample is irradiated with ions are of two types. One type is scattered while carrying an electric charge. The other type is scattered as a neutral particle since its electric charge is acquired by the sample. The aforementioned characterizing feature of the time-of-flight spectrometer derives from the fact that all of the scattered particles consisting of these two types are subjected to energy analysis.
Of the two types of particles mentioned, many of those that are scattered while possessing electric charge are caused to scatter by the atoms arrayed on the surface of the sample. On the other hand, the neutralized particles penetrate into the interior of the sample from its surface and are scattered after interacting with the atoms of the sample. In other words, the two types of particles possess different information regarding the sample.
Accordingly, the impact collision ion-scattering spectrometer apparatus which uses the time-of-flight spectrometer discards information specific to these two types of particles and obtains only that information common to both types of particles.
In terms of its structure, the features of the time-of-flight spectrometer are as follows:
The time-of-flight spectrometer includes an ion source and a detector arranged in a straight line on their common optic axis, with the detector being situated between the sample and the ion source. Accordingly, in order to perform energy analysis based upon time of flight, a considerable particle flight distance is required. As a result, the distance from the ion source to the sample surface is great and therefore it is difficult to make the beam converge on the sample surface. Consequently, the apparatus is not suited to micro-structural analysis of the sample surface and the only information acquired is average analytical information of certain areas.
Nevertheless, since the above-described apparatus possesses a linearly arranged structure, an advantage is that little space is required for installation.
Accordingly, regardless of the aforementioned drawback, namely the fact that the impact collision ion-scattering scattering spectrometer apparatus using the time-of-flight spectrometer is not suitable for micro-structural analysis of a sample surface, the apparatus is in wide use because the energy of all scattered particles is analyzed and because of the above mentioned advantage of the small installation space required.
The present applicant has disclosed, in the specification of Japanese Patent Application Laid-Open No. 63-102151, filed for patent in Japan on Oct. 17, 1986 and laid open on May 7, 1988, an impact collision ion-scattering spectrometer apparatus using the above-described time-of-flight spectrometer. In accordance with the disclosed apparatus, only ions scattered over a very wide scattering angle approaching 180.degree. are detected, and the scattered ions are not utilized sufficiently. In addition, particles cannot be distinguished by the absence or presence of electric charge, and therefore the analytical information indicative of the sample surface cannot be analyzed sufficiently. Furthermore, difficulties are encountered in converging the ion beam on the sample surface, the apparatus is not suited to micro-structural analysis of the sample surface, and the only information acquired is average analytical information of certain areas.
Similarly, the present applicant has disclosed, in the specification of Japanese Patent Application Laid-Open No. 63-102150, filed for patent in Japan on Oct. 17, 1986 and laid open on May 7, 1988, an impact collision ion-scattering spectrometer apparatus in which the ion beam is deflected and caused to perform scanning in two dimensions on the planar surface of a sample so as to analyze the composition of the sample surface. In this apparatus also, the scattered ions are not utilized sufficiently, just as in the example of the prior art described above. In addition, particles cannot be distinguished by the absence or presence of electric charge, and therefore the analytical information indicative of the sample surface cannot be analyzed sufficiently. Furthermore, difficulties are encountered in converging the ion beam on the sample surface, the apparatus is not suited to micro-structural analysis of the sample surface, and the only information acquired is average analytical information of certain areas.